What is the optimal air flow rate in fluid bed roasters?

[Warrior372]

Haha. I tried the blower / propane tube with the damper and at last success! I could maintain 350-500F pretty easily. I think the catch is I am just going to have to find a place inside to use this until it gets warmer outside. So, exhaust hose here we come. I am making the roasting chamber later today, so we will see if I can make this thing work!

[John F]

Can you turn off the heat and just use the blower to see what you can loft in green?

[Warrior372]

I can do that. I am still crafting a roasting chamber, so I will get back to you when I have  better idea of possible batch size. It will be nice as well, as I can just cut the propane blower and open the slide damper to cool the beans after roasting.

[John F]

It will be nice as well, as I can just cut the propane blower and open the slide damper to cool the beans after roasting.

Very slick. 

[Warrior372]

Alright. So I finally found something I think will work as a roasting chamber for the time being anyway. I love the shape, but wish it was made of thicker glass. I wonder if a local glass blower could make something. . . . I found it at Crate & Barrel of all places! That might convince some of you to go in next time the wife wants to stop .

I do not have a scale, so I took a bag of beans I knew was 5lbs and poured a little less than half into the roasting chamber. They blew around alright!  From the sound of things they should blow even more as they get further into the roasting process. The shape of the chamber works really well too! The beans blow up in the middle and slide down the sides.

I am wondering if I should just upgrade the propane torpedo to a 75k-100k now versus later. . . That would allow me to achieve proper roasting temps, eliminate the slide damper and just let the blower go full force. Not that I really have a need to roast more than 2 lbs of coffee at a time, but it would allow me to roast larger batches too. It would add another 85 dollars or so to a project that is already around $500-600. . . a little more than I wanted to spend. . . Any thoughts?

Here is a picture for all of you. I am going to add exhaust tubing so I can roast inside too. I still have to rivet the ducts together and wrap it in aluminum tape as well. There was air slightly leaking from an area or two, so that should help.

Cheers,
Michael

[Warrior372]

I am going to hook up exhaust tubing which will allow me to roast indoors. I am thinking about hooking up an exhaust duct booster to pull the smoke up into the exhaust tubing and push it out of the exhaust. Depending on the CFM of the duct booster would it also help suspend the beans in the roasting chamber? I am thinking it might. . . as there will be an air flow pull from above. . . Any thoughts?

Thanks!

[peter]

I use two duct boosters to exhaust smoke, one just above my roasting hood and the other one at the top of a 16' stack, which dumps into the attic.  They do a so-so job of venting smoke, but doubt that even both of them together would loft any beans.  Every couple months I have to clean the roastium of the blades or they suck even less.  Or put it another way, they suck even more.   

[Warrior372]

I have the roaster setup right next to my balconies siding glass door. I am just planning on opening the glass door and having a mount outside to hang the exhaust tubing from while roasting. The smoke might be traveling 5 feet total. Is there any reason to have a booster if it only needs to go 5 feet? With the the roasters blower on there is a considerable amount of air flow flying out of the roasting chamber already.

[J.Jirehs Roaster]

I have the roaster setup right next to my balconies siding glass door. I am just planning on opening the glass door and having a mount outside to hang the exhaust tubing from while roasting. The smoke might be traveling 5 feet total. Is there any reason to have a booster if it only needs to go 5 feet? With the the roasters blower on there is a considerable amount of air flow flying out of the roasting chamber already.

I am thinking you will not need any booster fan.... I would avoid drops droops in the line if it is flexy duct but at the speeds you are pushing that may not be an issue.. 

[Warrior372]

I call it the Squidmann. It kind of looks like the Cat and the Hat character from Dr. Suess!

So, I changed a few things around. I made a roasting chamber mount that allows me to clamp the roasting chamber into place. Also, in the top portion of the mount there is a built in bean screen, so beans can not fly out the exhaust, a chaff collecting chamber (which I made to resemble a Sono's), and the exhaust tube is mounted to the top as well. I riveted all of the tubing together so it is surprisingly stable. The top of the roasting chamber sits about 5 feet off of the ground, it should be fun to watch them progress through the roast! I am going to the hardware store in the AM to pick up flexible exhaust tubing, and that should be it. I again poured about 2.5 pounds into the chamber and the beans were flying about 5-6". Maybe it can handle 3lbs? I am not sure if they need to be flying that high. I will report back with final details.

Here is a picture of it in it's current state.

[grinderz]

Awesome, now we need video!

[Warrior372]

I am getting a little frustrated with the 'homemade' fluid bed roaster. The flame in the propane torpedo tube keeps going out a few seconds after I flick the blower on. I am not sure if the flame in the propane tube is not getting enough oxygen, if the air flow from the blower is just moving all of the oxygen too fast, or maybe if I just need to get an adjustable propane adapter so I can push more propane through. . . .

The 2 work just fine with one another until I put the roasting chamber in. Filled or not the flame in the propane tube blows out. . .

[J.Jirehs Roaster]

I am getting a little frustrated with the 'homemade' fluid bed roaster. The flame in the propane torpedo tube keeps going out a few seconds after I flick the blower on. I am not sure if the flame in the propane tube is not getting enough oxygen, if the air flow from the blower is just moving all of the oxygen too fast, or maybe if I just need to get an adjustable propane adapter so I can push more propane through. . . .

The 2 work just fine with one another until I put the roasting chamber in. Filled or not the flame in the propane tube blows out. . .

sounds like the roast chamber (or more likely the chaff collector) is chocking the blower and the blower is then back pressuring to the burner

[grinderz]

Too much airflow? Maybe you could install a rheostat or dimmer switch on the blower motor to slow it down?

[Warrior372]

Hmm. . . I am not sure how to do that. The blower and motor are quite large. The manufacturer said the only way to legitimately regulate the speed of the blower is through a belt drive. I am not mechanically inclined enough to think otherwise .

There is another issue now, I think I might just scrap the propane torpedo idea and try something else. There are slits in the outer shell of the propane tube, and with the new setup probably 75% of the blowers air is escaping through them.

I think I might purchase a high pressure cast iron propane burner, or a propane jet burner, and try to use that as the heat source. They burn up to 185,000 BTU and you can regulate the power with a propane adjustment adaptor. Something like this maybe?

http://www.turkey-fryers.com/SP-1_propane_patio_stove.htm

Any other ideas? Would a heat coil be easier?